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For 1990-2009 cars only
Makes 🢒 Chevrolet 🢒 2007 🢒 Lumina VE 🢒 Diagnostic Navigation 🢒 Vehicle Diagnostic Information 🢒 DTC P0420 or P0430

DTC Descriptor

DTC P0420: Catalyst System Efficiency Below Threshold (Bank 1)

DTC P0430: Catalyst System Efficiency Below Threshold (Bank 2)

Diagnostic Fault Information

Important: Always perform the Diagnostic System Check - Vehicle prior to using this diagnostic procedure.

Circuit/System Description

A 3-way catalytic converter (TWC) controls emissions by converting hydrocarbons (HC) and carbon monoxide (CO) into CO2, and oxides of nitrogen (NOx) into nitrogen. The TWC also stores oxygen. The engine control module (ECM) monitors this oxygen storage capacity by comparing the pre and post-catalyst oxygen sensor signals while adding and subtracting fuel during specific idle conditions. The ECM compares the engine and catalyst oxygen sensor signals in order to determine if the oxygen storage capacity of the catalyst is degraded.

Important: A new converter with less than 100 miles on it may set P0420 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

If the ECM detects the degraded condition DTC P0420 sets.

Conditions for Running the DTC
    • DTCs P0030, P0036, P0068, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0120, P0121, P0122, P0123, P0130, P0131, P0132, P0133, P0134, P0135, P0137, P0138, P0140, P0141, P0171, P0172, P0201, P0202, P0203, P0204, P0205, P0206, P0207, P0208, P0220, P0300, P0315, P0326, P0327, P0336, P0340, P0341, P0506, P0507, P0601, P0602, P1133, P1516, P1621, P2135, P2138 orP2176 are not set.
    • DTCs P0031, P0037, P0038, P0106, P0107, P0108, P0112, P0113, P0117, P0118, P0122, P0123, P0125, P0128, P0130, P0131, P0132, P0133, P0134, P0137, P0138, P0140, P0141, P0171, P0172, P0300, P0326, P0327, P0336, P0340, P0341, P0500 (manual transmission only), P0506, P0507, P0601, P0602, P0606, P0641, P0722, P0723 o rP1133 are not set.
    • The engine has been running for more than 450 seconds.
    • The vehicle has been driven at more than 1,000 RPM for more than 1 minute.
    • The vehicle speed is less than 3.2 km/h (2 mph).
    • The vehicle is in Closed Loop.
    • For automatic transmissions, the transmission is in Reverse, Drive or Low.
    • The engine coolant temperature (ECT) is between 70-125°C (156-257°F).
    • The barometric pressure (BARO) is more than 70 kPa.
    • The catalytic converter calculated temperature is greater than or equal to 480°C (896°F).
    • The intake air temperature (IAT) is between -20 and +85°C (-4 and +185°F).
    • The battery voltage is more than 11 volts.
    • The throttle position (TP) is 2 percent or less.
    • The short term fuel trim (FT) is between -10 and +10 percent.
    • This diagnostic attempts one test during each valid idle period when the above conditions have been met. This diagnostic attempts up to 6 tests during each drive cycle.

Conditions for Setting the DTC
    • The ECM has determined the catalyst efficiency has degraded below a calibrated threshold.
    • This diagnostic may conclude in as few as one test attempt. However this diagnostic may require as many as 18 test attempts, which would require at least 3 drive cycles. Each test attempt may conclude within approximately 1 minute.

Action Taken when the DTC Sets

DTC P0420 or P0430 are type B DTCs.

Conditions for Clearing the MIL/DTC

DTCs P0420 or P0430 are type B DTCs.

Diagnostic Aids
    • Inspect for the following conditions, which may cause a catalytic converter to degrade:
       - An engine misfire.
       - High engine oil or high coolant consumption.
       - Retarded spark timing.
       - A weak or poor spark.
       - A lean fuel mixture.
       - A rich fuel mixture.
       - A damaged oxygen sensor or wiring harness.
       - The catalyst test may abort if the vehicle falls outside the conditions for running the DTC.
       - A catalyst may be temporarily degraded if a fuel with high sulfur content has been used. Drive the vehicle at highway speeds for 10 minutes and retest the converter.
    • If an intermittent condition cannot be duplicated, the information included in the Freeze Frame Records can be useful in determining the vehicle operating conditions when the DTC was set.
    • If the condition is determined to be intermittent, refer to Testing for Intermittent Conditions and Poor Connections .

Reference Information

Electrical Information Reference

Diagnostic Trouble Code (DTC) List - Vehicle .

Circuit/System Verification

Operate the vehicle within the Conditions for Running the DTC.

⇒If the DTC fails this key cycle, proceed with Circuit/System Testing.

Circuit/System Testing

Notice: Refer to Silicon Contamination of Heated Oxygen Sensors Notice in the Preface section.

Important: A new converter with less than 100 miles on it may set P0420 or P0430 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

  1. Inspect the catalytic converter for the following conditions:
    2. • Dents.
    • A severe discoloration caused by excessive temperatures.
    • Road damage.
    • An internal rattle caused by damaged catalyst substrate.
    • Restrictions.
         ⇒If a condition is found, replace the catalytic converter.
  2. Inspect the exhaust system for the following conditions:
    3. • Leaks.
    • Physical damage.
    • Loose or missing hardware.
    • Properly torqued HO2S.
         ⇒If a condition is found, repair the exhaust system.
  3. Inspect the HO2S 2 for the following conditions:
    4. • A grounded wiring harness.
    • Damage.
         ⇒If a condition is found, replace the HO2S 2.
         ⇒If no physical condition is detected, replace the catalytic converter.

Repair Instructions

Important: A new converter with less than 100 miles on it may set P0420 or P0430 due to out-gassing of the internal matting. Operating the vehicle at highway speeds for approximately 1 hour may correct the condition.

    •  Exhaust Manifold Replacement - Left Side .
    •  Exhaust Manifold Replacement - Right Side .
    •  Heated Oxygen Sensor Replacement - Bank 1 Sensor 2 .
    •  Heated Oxygen Sensor Replacement - Bank 2 Sensor 2 .
    •  Exhaust Leakage .
    •  Restricted Exhaust .
    •  Engine Control Module Replacement for engine control module replacement, setup and programming.

Repair Verification
  1. Operate the vehicle within the Conditions for Running the DTC.
  2. Verify if DTC P0420 or P0430 has passed or failed this ignition cycle with the scan tool.
  3. If 6 tests have been attempted and the DTC has not run or passed during this key cycle, key to OFF for 30 seconds then run the test a second time.
  4. A maximum of 6 tests per key cycle will run if each test is a combination of passed, failed or aborted tests.

    5. Important: DO NOT touch the accelerator, the HVAC or the steering wheel while a catalyst test is in progress.

  5. After a code clear, the catalyst test will run once if the test is a pass.
  6. Allow the engine to return to a stabilized idle. Keep the vehicle in DRIVE.